Here is my guided video, but for those who want a verbal walkthrough:
1. Load the first campaign area: IPSILON.
2. Load the first mission.
*You may have to beat it the regular way the first time.*
3. Delete everything by pressing x while hovering over the item, except the middle grey cube.
4. Use one of the top buttons to "set the machine on the ground".
5. Make a flat square out of wood.
6. Place the flamethrower along the ground attached to the vehicle.
7. Put wood right in front of the flamethrower nozzle that is attached to the vehicle.
8. Start the level.
8. Shoot the flamethrower, and the entire vehicle will catch on fire.